1. Field of the Invention
The present invention relates to an exposure determining device which determines the proper amount of exposure for each primary color in printing a picture of a color negative film on a color paper or in printing a picture of a monochrome film on a variable contrast paper such as Poly contrast paper (Eastman Kodak Co.), Varigam (Du Pont Co.,), Multigrade (Ilford Co.), and multitone Yoshino (Konishiroku Co.), the determined amount of exposure being used for controlling the amount of light to be emitted from the light source of an enlarger and or indication of the proper amount of exposure of the enlarger or the amount of light emission from the light source thereof.
2. Description of the Prior Art
In order to obtain a proper color print from a color negative film, the following method has been known. At first, a predetermined standard negative film is printed in various exposure conditions until a best print, i.e., a print that is thought or judged as best, is obtained. Under the condition where the best print is obtained, the amount of exposure and the color balance on the easel of the enlarger are measured with a color balance indicating device such as shown in U.S. Pat. No. 4,205,918. Next, a color negative film to be printed is set in the enlarger instead of the standard negative film. Then, under the condition where the color negative film to be printed (hereinafter, called the printing negative film) is set, the amount of exposure and the color balance on the easel are measured with the color balance indicating device again. The light intensity and the color balance of the light emitted from the light source of the enlarger is controlled so that the amount of exposure and the color balance measured for the printing negative film are coincided with that measured for the standard negative film.
However, the above conventional device is constructed to measure a specific area of an image formed on the easel because the light receiving surface of the device is smaller than the area in which the image would be formed. Therefore, in the conventional method, the exposure amount and the color balance within a specific area of the image of the printing negative film are compared with the exposure amount and the color balance within a specific area of the image of the standard negative film. Therefore, if the condition for a measuring point for the image of the printing negative film is different from the condition for a measuring point for the image of the standard negative film, a proper color print would not be obtained for the printing negative film. For example, with respect to both measuring points on the images of the standard and printing negative films, if a measuring point is selected for shadow portion of an image and another measuring point is selected for high light portion of another image, or if the persons photographed on each negative films are conspicuously different in skin color from each other although both measuring points are selected for the skins of the persons photographed on each negative film, the above impropriety would occurred.
To avoid this, it is necessary that the printing negative film has an area on which the condition is the same as the condition on the measuring point for the standard negative film and that such area on the printing negative film must be found out by an operator. Namely, the above impropriety would be avoided by setting the measuring point for the printing negative film on the image of such area. However, it takes skill to find out, in the printing negative film, the area on which the condition is the same as the condition of the measuring point for the standard negative film, and to locate the light receiving surface of the color balance indicating device on the image of said area. Furthermore, in this method, it must be required for the operator to memorize the condition on the measuring point for the standard negative film, and such requirement is an inconvenience for the operator.
On the other hand, another method for obtaining a proper color print from the printing negative film has been known. In such method, the whole image of the printing negative film is recognized as a pattern in order to judge how the printing negative film has been photographed (for example, whether the film has been photographed in a room or outdoors, or whether the film has been photographed under the daylight or under the flash light). The proper amount of exposure and the proper color balance in printing the printing negative film is determined in accordance with the result of the judgement. Nevertheless, in this case, when the reproduction of the specific part in the picture is desired, no proper indication for such a small portion will be provided because such method is to measure the entire of the picture image. Accordingly, the adjustment of the light source can be made only by a skilled operator who observe the negative film image and determine the exposure condition based on his experience.